Exchange and oxidation of CO on O-predosed Rh---Al2O3 and Rh---CeO2 catalysts

Exchange and oxidation of C¹⁶O were investigated at 450°C on ¹⁸O-predosed Rh and Pt catalysts supported on A1₂O₃, CeO₂ and CeO₂-Al₂O₃. In all cases, a rapid exchange of C¹⁶O with the surface can be observed. CO oxidation leads to C¹⁶O₂, C¹⁶O¹⁸O and C¹⁸O₂. Significant formation of C¹⁶O₂ is due to the relatively high ¹⁶O coverage in reaction resulting from the C¹⁶O exchange and from an exchange between O surface species and ¹⁶O internal atoms. Hydrogen is also formed via a water-gas shift reaction (CO + surface OH) in higher proportion on CeO₂-containing catalysts than on A1₂O₃. Chlorine inhibits all the reactions (exchange, oxidation and WGS) and particularly the internal exchange.     

Enhanced electron emission from phosphorus-doped diamond-cladsilicon field emitter arrays

Undoped and phosphorus (P)-doped diamond-clad Si field emitter arrays have been successfully fabricated using microwave plasma chemical vapor deposition (MPCVD) technology. The electron emission from the blunt diamond-clad microtips are much higher than those for the pure Si tips with sharp curvature due to a lower work function. Furthermore, the characteristics of emission current against applied voltage for the P-doped diamond-clad tips show superior emission at lower field to the undoped ones. After the examination of Auger electron spectroscopy (AES) and electrical characteristics of as-grown diamond, such a significant enhancement of the electron emission from the P-doped diamond-clad tips is attributed to a higher electron conductivity and defect densities     

Determination of the width of the transition layer between the crystalline and amorphous zones in nylon 1010 by SAXS

The width of the transition layer between the crystalline and amorphous zones in nylon 1010 was determined by SAXS with point collimation and long-slit collimation, respectively. The width of the transition layer, E, was found to be 1.7 nm. The results show that the width of the transition layer is independent of crystallinity.     

Cumulant calculations of thermodynamic quantities for the Hubbard and the emery model

The calculations of the first paper suggesting phase separation in the Hubbard model [2] are performed under modern computer facilties for the one and three-band Hubbard model. High-temperature approximations for specific heat and static correlation functions are obtained. The latter show, at these high temperatures, no tendency to phase separate in the same way as in the cited paper because our spin parallel nearest-neighbor charge correlation function is negative for all doping values. The spin antiparallel correlation function has positive and negative values for different doping regimes.Extension of this work to higher levels of iterations and to other correlation functions is in progress.     

Propagation of a quasi-shear horizontal acoustic wave in Z-Xlithium niobate plates [and conductivity sensor application]

It is found that an acoustic wave which is nearly polarized in the shear horizontal (SH) direction can propagate along the X axis of a Z-cut lithium niobate plate if the ratio h/λ, where h=plate thickness and λ=acoustic wavelength, is less than about 0.5. Attractive properties of this quasi-SH wave include: (1) phase velocity nearly constant for all values of h/λ; (2) ability to propagate in contact with a liquid medium; and (3) electromechanical coupling coefficient as high as 0.15. These properties make the wave attractive for use in a variety of sensor and signal processing applications. An example of sensor applications is illustrated by using the wave to measure conductivity of liquids (aqueous KCl solution). The frequency of a 12-MHz quasi-SH mode oscillator fabricated on a 0.48 wavelength thick Z-X lithium niobate plate is found to vary by more than 80 kHz for variation in KCI concentration from 0 to 0.15%     

The information-theoretic capacity of discrete-time queues

The information-theoretic capacity of continuous-time queues was analyzed recently by Anantharam and Verdu (see ibid. vol.42, p.4-18, 1996). Along similar lines, we analyze the information-theoretic capacity of two models of discrete-time queues. The first model has single packet arrivals and departures in a time slot and independent packet service times, and is the discrete-time analog of the continuous-time model analyzed by Anantharam and Verdu. We show that in this model, the geometric service time distribution plays a role analogous to that of the exponential distribution in continuous-time queues, in that, among all queues in this model with a given mean service time, the queue with geometric service time distribution has the least capacity. The second model allows multiple arrivals in each slot, and the queue is modeled as serving an independent random number of packets in each slot. We obtain upper and lower bounds on the capacity of queues with an arbitrary service distribution within this model, and show that the bounds coincide in the case of the queue that serves a geometrically distributed number of packets in each slot. We also discuss the extremal nature of the geometric service distribution within this model     

Multi-emitter Si/GexSi1-x heterojunctionbipolar transistor with no base contact and enhanced logic functionality

We demonstrate multi-emitter Si/Ge_xSi_1-x n-p-n heterojunction bipolar transistors (HBT's) which require no base contact for transistor operation. The base current is supplied by the additional emitter contact under reverse bias due to the heavy doping of the emitter-base junction. Large-area HBT test structures exhibit good transistor characteristics, with current gain β≈400 regardless of whether the base current is supplied by a test base electrode or one of the emitter contacts. These devices have enhanced logic functionality because of emitter contact symmetry. Since device fabrication does not require base electrode formation, the number of processing steps can be reduced without significant penalty to HBT performance     

Penetrating ocular injuries: an epidemiologic and retrospective study

Penetrating injuries of the eye are an important cause of unilateral visual loss. We studied a series of 82 cases of penetrating injuries treated here from 1987 through 1993. The injuries were caused by sharp objects in 66% and blunt trauma in 6%. The prognosis after a penetrating injury is greatly influenced by the nature of the injury and the extent of the initial drainage. Among factors associated with an unfavorable visual outcome were diminished preoperative visual acuity and scleral wounds with dense vitreous hemorrhage.     

Cardiovascular anatomy and physiology in the female

A flow-injection analysis method for the determination of albumin tannate in tablets is reported. After optimization of the variables involved, the method has been characterized and validated in terms of calibration using three procedures: repeatability and reproducibility; ruggedness; and selectivity. Finally, it has been applied to real samples (tablets).